Electric-field-induced anti-Stokes photoluminescence in an asymmetric GaAs/(Al,Ga)As double quantum well superlattice

We have used photoluminescence (PL) spectroscopy to study the population properties of an asymmetric GaAs/(Al,Ga)As double quantum well superlattice, which represents a simplified version of the active region of a quantum cascade laser. The investigation focuses on the anti-Stokes PL signal of the narrower well, which is observed for excitation between the excitonic states of the two quantum wells and sufficiently high electric field strengths. In this case, the photocarriers are only excited in one of the two wells, and the signal gives direct evidence for transport of electrons and holes through the (Al,Ga)As barriers. An analysis of the electric-field dependence of conventional PL as well as anti-Stokes PL demonstrates that population inhomogeneities for the electronic states can be determined.